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RE: WARNING against using Staples in shear walls/diaphragms

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David,
In addition to the fact that the ability of staples to resist cyclical loads
has not been determined by test, I believe that the following considerations
indicate that they should not be permitted for shearwalls:
1) There are additional problems with quality control because you cannot see
by inspection if the staple has penetrated the support member or merely bent
over at its surface under the sheathing;
2) In post-disaster evaluation, it is very difficult to see if the staple
has sheared off behind the sheathing, whereas a nail would be visibly bent
out of its original position;
3) Unlike nails, the staples lack ductility to bend without breaking;
4) Staples are much more subject to corrosion than nails because of their
thin cross section.
This has been discussed at length at SEAOC Code Committee meetings and all
of those present have agreed to this position.  This conclusion, like any
other, could be found incorrect if adequate testing proves otherwise; and
that testing should be done.  However I think that prohibiting them on the
basis of what we now know is prudent.
Richard Hess, SE

-----Original Message-----
From: mrkgp(--nospam--at)winfirst.com [mailto:mrkgp(--nospam--at)winfirst.com]
Sent: Wednesday, February 06, 2008 8:10 AM
To: SEAINT
Subject: WARNING against using Staples in shear walls/diaphragms


My first impression of stapling plywood is that it may be a better system
than nails. Design factors may need to be re-considered. My strongest
concern is corrosion of the staple, not its resilience in a seismic event. A
water repair should include a review of the staples.

Following are what I intend to find answers for and these are followed by
some facts that can help.

What spans are the drift values for?
When is the drift limited by the gaps between the panels edges?

If drift exceeds 1", how probable is it to not witness a permanent
deflection? Is a nailed diaphragm allowed to remain if there is evidence of
a 1" drift?

Over the shorter distance of the staple drift could the staple demonstrate a
higher resistance than the nail and absorb more energy? Could more staples
develop this equivalent energy absorption?

What are the COLA/SEAOSC and CUREE test methods as they relate to the above
questions.

I have talked to a contractor who I had remove a stapled diaphragm. The
stapled plywood, was twice as difficult to remove than a similar nailed
system. That suggests that when panel edges bind it might be more likely for
a nailed panel to separate, out of plane, from the framing.

Like gypsum, there might need to be more staples. Gypsum, with the proper
design penalties and correctly installed, can out perform the equal plywood
option.

Lately I have heard of testing of shear walls, at SJSU. Inadvertently, they
discovered the shear wall nails were not yielding before the hold-downs
failed. That probably results in little energy absorption. Could it be that
we cannot rely on the code design benefits of nail yielding when brittle
hold-downs trump the energy absorbing capacity?

David B Merrick, SE

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